Prevention of liquid backflow into gas compressor



Nov. 11, 1969 L. s. KITCHEN ETAL 3,477,457

PREVENTION OF LIQUID BACKFLOW INTO GAS COMPRESSOR Filed Nov 15. 1967 f)N Q T- W A 0 R5 5 0 I m Q N "I N 00 F v I "L' I E I 15, I W O m I 5" 1a: 5 N

INVENTORS L. G. KITCHEN BY K. G. RHEA A 7' TORNEYS United States Patent3,477,457 PREVENTION OF LIQUID BACKFLOW INTO GAS COMPRESSOR Leland G.Kitchen and Keith G. Rhea, Bartlesvllle, Okla., assignors to PhillipsPetroleum Company, a corporation of Delaware Filed Nov. 15, 1967, Ser.No. 683,284 Int. Cl. F04f l /'18 US. Cl. 137-209 9 Claims ABSTRACT OFTHE DISCLOSURE The output of a gas compressor is passed through achamber containing a liquid level switch and then through aconduitcontaining a control valve and into a liquid pipeline. A differentialpressure controller measures the differential pressure across thecontrol valve and actuates a three-way valve to pass the output of theliquid level switch to the control valve when the differential pressureis below a predetermined value and actuates the three-way valve toconnect an air supply to the control valve when the differentialpressure exceeds the predetermined value.

This invention relates to method and apparatus for controlling a valvein the discharge line of a gas compressor to a liquid line. In pastsystems it has been the practice to utilize a check valve in thedischarge line to prevent flow of liquid from the liquid line to the gascompressor when the gas compressor is shut down or has its outletbypassed to its inlet to stop gas flow through the discharge line.However, it is not uncommon for check valves to have small leaks whenthe pressure across the valve is small. Even small leaks permit anaccumulation over a period of time of enough liquid to severely damagethe gas compressor.

Accordingly, it is an object of the invention to provide improved methodand apparatus for preventing liquid backflow in a discharge line from agas compressor into a liquid line. Another object of the invention is toprotect a gas compressor from liquid entering the discharge conduit.

Other objects, aspects and advantages of the invention will be apparentfrom a study of the specification, the drawing and the appended claimsto the invention.

Referring now to the drawing, which is a diagrammatic representation ofone embodiment of the invention, a gas is passed through conduit 11 intothe inlet of compressor 12. Bypass conduit 13, containing valve 14,communicates between the outlet of compressor 12 and the inlet ofcompressor 12. Valve 14 is manipulated by pressure recorder controller15 responsive to a comparison of the desired pressure at the inlet ofcompressor 12 as represented by setpoint 16 with the actual pressure atthe inlet of compressor 12 as indicated by pressure sensor 17. Thus, theposition of valve 14 is varied to maintain the inlet pressure oncompressor 12 substantially constant at the desired value. Conduit 18communicates between the outlet of compressor 12 and an upper portion ofvertically elongated tank 19. Conduit 21, containing a control valve 22,communicates between a lower portion of tank 19 and liquid transferconduit 23, containing a pump 24. Liquid level switch 31 has a floatelement 32 positioned within tank 19. Conduit 33 supplies high pressureair to an inlet of liquid level switch 31. When the liquid level in tank19 is below the switching position of float 32, liquid level switch 31passes air from conduit 33 through line 34 to one inlet of three-wayvalve 35. When the liquid level in tank 19 3,477,457 Patented Nov. 11,1969 7 through output line 38 to valve 22. When valve 35 is in itssecond position, conduit 36 is connected through line 38 to valve 22.The presence of high pressure air in line 38 causes normally closedcontrol valve 22 to open while the absence of high pressure air in line38 causes valve 22 to close.

Differential gap controller 41 has first and second inlets thereofconnected to conduit 21 upstream and downstream, respectively, of valve22 to determine the differential pressure across valve 22. Controller 41has a setpoint or threshold adjustment 42 and a gap adjustment 43.Controller 41 effectively serves as an on-off controller wherein an onoutput signal is initiated whenever the positive differential pressureacross valve 22 exceeds the predetermined positive threshold valuerepresented by setpoint 42. The term positive indicates that thepressure upstream (on the gas compressor side) of valve 22 is greaterthan the pressure on the downstream (conduit 23) side of valve 22. Theon output signal then continues until such time as the positivedifferential pressure across valve 22 drops below a cut-off valuerepresented by gap adjustment 43. The cut-off value is less than thethreshold value to provide a gap or dead band. The on output ofcontroller 41 actuates three-way valve 35 to its second position whilethe off output (absence of on) of controller 41 actuates valve 35 to itsfirst position, described hereinabove.

In the operation of the system, assume the valve 14 is open to fullyrecycle the output of gas compressor 12. Valve 22 will be closed andtank 19 will contain liquid up to the switching level of liquid levelswitch 31. The pressure on both sides of control valve 22 will besubstantially equal. The differential pressure across valve 22 will beless than the threshold value of setpoint 42, controller 41 will have anoff output, and valve 35 will be in its first position to connect line34 to valve 22 while liquid level switch 31 connects line 34 to vent.When the fresh supply to compressor 12 becomes sufiicient, valve 14 willat least partially close, causing the pressure in tank 19 and conduit 21upstream of valve 22 to increase. When the output pressure of compressor12 builds up enough for the differential pressure across closed controlvalve 22 to reach the positive threshold valve 42, controller 41produces an on output signal, actuating three-way valve 35 to its secondposition. This results in the passage of high pressure air from conduit36 to valve 22, causing valve 22 to open. The gas output of compressor12 pushes the liquid out of tank 19 and conduit 21 into line 23. Thedrop in liquid level actuates liquid level switch 31 to connect line 34to high pressure air supply 33. The movement of the liquid through valve22 results in a dropping of the pressure drop across valve 22. When thedifferential pressure across valve 22 decreases to the cut-off value,controller 41 actuates three-way valve 35 to its first position,connecting line 34 to valve 22. The high pressure air now available inline 34 from conduit 33 maintains valve 22 in the fully open position.

At such time as the fresh gas supply to compressor 12 becomesinsufficient, valve 14 is opened to recycle the output of compressor 12,dropping the pressure in tank 19. The lowered pressure permits liquidfrom line 23 to pass through conduit 21 into tank 19. When the level ofliquid in tank 19 reaches the switching level of float 32, switch 31transfers line 34 from air supply 33 to vent, thus venting line 38 andcausing valve 22 to close. At the time the valve 22 closes, thedifferential pressure thereacross is less than positive threshold valve42 and con troller 41 continues its off output.

While valve 22 has been described as a normally closed, spring biasedvalve requiring positive air pressure to open, other types of valves canbe utilized. If necessary, or desirable, line 38 can be connected to apilot valve which controls the position of valve 22. While the controlsystem has been described in terms of pneumatic components, mechanical,electrical or electro-mechanical components can be employed. Suitablepneumatic examples of switch 31 and controller 41 are the liquid levelswitch model 2820C-252V, manufactured by the Fisher Governor Company,and differential gap controller model X 162R, manufactured by the TaylorInstrument Company. A high gain controller having a narrow band or abiased pilot valve could be utilized instead of controller 41. While thepressure sensing lines to controller 41 are shown as connected toconduit 21 closely adjacent to valve 22, the upstream pressure sensingline can be connected to tank 19 or conduit 18, and the downstreampressure sensing line can be connected to liquid transfer line 23.

Reasonable variations and modifications are possible within the scope ofthe foregoing disclosure, the drawing and the appended claims to theinvention.

We claim:

1. Apparatus for introducing compressed gas into a body of liquidcomprising a gas compressor, means containing a body of liquid, conduitmeans communicating between the outlet of said compressor and the liquidcontaining means, a first valve means operatively connected in saidconduit means, a liquid sensor switch operatively connected in saidconduit means so as to be actuated by liquid passing through saidconduit means from said liquid containing means before such liquidreaches said gas compressor, a power source, and control means fordetermining the differential pressure across said first valve means insaid conduit means and for passing the output of said liquid sensorswitch to said first valve means to control the position of said firstvalve means until said dilferential pressure exceeds a firstpredetermined value and for connecting said power source to said firstvalve means to open said first valve means upon said diiferentialpressure exceeding said first predetermined value and then disconnectingsaid first valve means from said power source and reconnecting saidfirst valve means to said liquid sensor switch upon said differentialpressure decreasing to a second predetermined value.

2. Apparatus in accordance with claim 1 wherein said first valve meansis positioned in said conduit means between said liquid sensor switchand said liquid containing means.

3. Apparatus in accordance with claim 2 wherein said liquid containingmeans comprises a pressurized liquid transfer conduit, and said liquidsensor switch is a liquid level switch.

4. Apparatus in accordance with claim 3 wherein said liquid level switchproduces a first output signal when the level of liquid in said conduitmeans exceeds the switching level of said liquid level switch and asecond output signal when said level of liquid is less than saidswitching level; and wherein said control means comprises differentialpressure sensing means for determining the difierential pressure acrosssaid first valve means and producing a first output signal when thepresure upstream of said first valve means exceeds the pressure in saidliquid transfer conduit by a predetermined positive value and producinga second output signal in the absence of said first output signal ofsaid difierential pressure sensing means, switching means having firstand second inputs and an output, means for connecting the output of saidliquid level switch to said first input of said switching means, meansfor connecting said power source to said second input of said switchingmeans, means for connecting said output of said switching means to saidfirst valve means to control the position of said first valve means,means responsive to said first output signal of said diiferentialpressure sensing means to actuate said switching means to connect saidsecond input of said switching means to said output of said switchingmeans and responsive to said second output signal of said differentialpressure sensing means to actuate said switching means to connect saidfirst input of said switching means to said output of said switchingmeans, either of the connection of said power source through said outputof said switching means and the connection of said second output signalof liquid level switch through said output of said switching meanscausing said first valve means to be fully opened.

5. Apparatus in accordance with claim 4 wherein said switching meanscomprises a three-way valve, said power source is a source of fluidpressure, and wherein said liquid level switch connects said first inputof said switching means to a source of fluid pressure to produce saidsecond output signal of said liquid level switch and connects said firstinput of said switching means to a vent to produce said first outputsignal of said liquid level switch.

6. Apparatus in accordance with claim 5 wherein said first valve meanscomprises a spring biased, normally closed valve.

7. Apparatus in accordance with claim 5 wherein said differentialpressure sensing means comprises a differential gap controller having athreshold setpoint and a cutoff setpoint.

8. Apparatus in accordance with claim 5 wherein said conduit meanscomprises a vertically elongated tank, said liquid level switch beingconnected in said tank, a first conduit connected between said outlet ofsaid gas compressor and the upper portion of said tank above said liquidlevel switch, and a second conduit connected between the lower portionof said tank and said liquid transfer conduit.

9. Apparatus in accordance with claim 8 further comprising a thirdconduit connected between said outlet of said gas compressor and theinlet of said gas compressor, a valve positioned in said third conduit,and means for manipulating said valve in said third conduit responsiveto the pressure at the inlet of said gas compressor.

References Cited UNITED STATES PATENTS 12/1957 Clifford 137-209 X 8/1967Lebow 137-389

